EFFECTS OF SHADE, IRRIGATION AND MYCORRHIZAL INOCULATION ON THE GROWTH, ESTABLISHMENT, AND DEVELOPMENT OF CACAO (THEOBROMA CACAO L.) SEEDLINGS

Abstract

Three experiments were conducted between 2009 and 2014 in both nursery and on the field to investigate the effects of shade and irrigation regimes and arboscular mycorrhizal fungi (AMF) inoculation on the growth, field establishment and development of cocoa (Theobroma cacao) seedlings at the Teaching and Research Farm, Federal University of Technology, Akure. The first experiment which was conducted between January to April, 2009, and repeated in January to April, 2010, evaluated the effects of time of AMF inoculation on root development, growth and vigour of cacao seedlings in the nursery. The experiment was a completely randomized design with four replications in which cacao seeds were inoculated at varying weeks after sowing (WAS): 0,(at sowing), 4, 8, 12 and 16 WAS. The results showed that inoculating seeds at sowing time (0 week), 4 and 8 WAS enhanced root and shoot development over the non-inoculated control. Significantly higher number of lateral roots, total leaf area per plant, number of leaves, and plant height were obtained with 0, 4, and 8 WAS compared with 12, and 16 and the non-inoculated control. The second experiment evaluated the effects of plantain shade and AMF inoculation on growth, establishment and survival of dry season field grown cacao seedlings between October 2009 and May 2010 and October, 2010 to May, 2011. The experiment was a randomized complete block design with six treatments replicated three times. The ratio of plantain (shade plant) to cacao was two rows of cacao to one row of plantain. The treatments involved were Shade + AMF inoculation @ nursery, Shade +AMF inoculation @ transplant, Shade alone, AMF inoculation @ nursery, AMF inoculation @ transplanting and non-inoculated control. Data were collected on the growth variables and survival count of cacao at 4 weeks interval. The results showed that shaded seedlings that were inoculated from the nursery had better performance at 7 month after transplanting (MAT) in May, 2011 in terms of plant height, stem girth, number of leaves and percent survival compared to seedlings inoculated at point of transplanting. Significantly lower values of measured growth parameters were obtained for the unshaded non-inoculated (No AMF) seedlings compared with the AMF inoculated seedlings for plant height, stem girth, number of leaves and percent survival. The percentage survival were 60, 28, 36 and 9 for Shade + AMF, AMF alone, Shade alone and no shade non inoculated control respectively. The third experiment examined the effects of shade and irrigation regimes and AMF inoculation on growth, field establishment and development of cacao transplanted between June, 2012 and April 2014. The experiment which was a 3x2x2 factorial combinations with three replications and laid out in a split plot design, examined the effects of shade regimes, (moderate, dense and no shade/open sun), irrigation regimes (5 and 10-day irrigation intervals) and AMF inoculation (with or without AMF inoculation). The results showed that shade-irrigation combinations promoted the vigour of cacao seedlings in terms of height, stem diameter, number of leaves and branches as well as the percent survival. Irrigation at 5 and 10 days intervals significantly increased percent survival from maximum of 60 % obtained in experiment 2 (shade-AMF combinations), to over 90 %. More so, cacao growth parameters were enhanced under no shade + AMF + irrigation combination in term of plant height, stem girth, number of leaves and number of branches. Improvement in cacao canopy development as measured by leaf area index (LAI) and intercepted photosynthetic active radiation (PAR) were higher in no shade (open sun) compared with moderate and dense shade treatments. In addition, total shoot biomass, flower and pod production were best for the unshaded but irrigated seedlings compared with shade + irrigation treatments. The unshaded+ irrigated plants had higher radiation use efficiency (RUE) compared with shaded + irrigated and RUE values were significantly higher for 5-day irrigation interval compared with 10-day irrigation interval over moderate and dense shade treatments. Cacao growth was negatively affected by shade treatment in term of height, stem girth, number of leaves and number of branches which were significantly lower compared to values from no shade plots. Moderate and dense shade improved soil moisture contents and reduced soil temperatures during the dry season compared with the no shade treatments in combination with irrigation. Air temperature within the canopies of cacao under shade were lower than those in open sun. The transmitted radiation and intercepted PAR values within plantain shades to canopies were lowest under dense shade. The low light intensities and LAI for under-storey cacao had negative implications for growth and biomass development.